Problem: Emily is 2 times as old as Umaima. 24 years ago, Emily was 8 times as old as Umaima. How old is Umaima now?
Explanation: We can use the given information to write down two equations that describe the ages of Emily and Umaima. Let Emily's current age be $e$ and Umaima's current age be $u$ The information in the first sentence can be expressed in the following equation: $e = 2u$ 24 years ago, Emily was $e - 24$ years old, and Umaima was $u - 24$ years old. The information in the second sentence can be expressed in the following equation: $e - 24 = 8(u - 24)$ Now we have two independent equations, and we can solve for our two unknowns. Because we are looking for $u$ , it might be easiest to use our first equation for $e$ and substitute it into our second equation. Our first equation is: $e = 2u$ . Substituting this into our second equation, we get: $2u$ $-$ $24 = 8(u - 24)$ which combines the information about $u$ from both of our original equations. Simplifying the right side of this equation, we get: $2 u - 24 = 8 u - 192$ Solving for $u$ , we get: $6 u = 168.$ $u = 28$.